Our research has revealed an unexpected aspect of the biology of the pattern recognition receptor, TLR-4. This molecule is expressed in the liver, principally on Kupffer cells. The engagement of liver TLR-4 by endotoxin derived from the intestinal bacteria promotes the expression of adhesion molecules in the hepatic sinusoids. Our Preliminary Data show that the TLR-4-dependent trapping of CD8+ T cells in the liver limits the size of systemic immune responses, and also of memory responses. In this proposal, we will test whether this mechanism can be exploited to enhance the effectiveness of a vaccine. Thus, we will prime influenza-specific CD8+ T cells either in mice congenitally lacking TLR-4, or in mice treated with Eritoran, a TLR-4 inhibitor that is already sanctioned for use in humans with severe sepsis. If this project is successful, we will have obtained proof-of-concept data that justify a new concept in vaccine biology. We term this the "reverse adjuvant" strategy, since it promotes CD8+ T cell responses via the inhibition of a molecule that more commonly acts to enhance immune responses. PUBLIC HEALTH RELEVANCE: Many important diseases, including malaria, hepatitis and AIDS, could be eliminated by successful vaccines. However, such vaccines are elusive. This project aims to develop a new approach to making vaccines more effective.